1. Technical Field of the Invention
This invention relates in general to electrical contacts, and particularly to a contact adapted for insertion into a plated hole in a printed circuit board.
2. Description of the Prior Art
Circuit board contacts which include a body portion for connection to an electrical device and a mounting portion adapted for insertion into a conductively plated through-hole in a circuit board are well known in the electrical arts and assume a variety of configurations. A first type is described in U.S. Pat. No. 2,994,057 and includes a solid mounting portion provided with ridged fins which is press fitted into the circuit board hole. This type of contact has not proven suitable since the circuit board is relatively fragile and is easily damaged by the high radial and axial forces produced during the press fitting operation and because the fins tend to dig into and injure the hole plating.
An improved contact of this type is described in U.S. Pat. No. 3,827,004 in which the mounting portion of the contact is generally H-shaped with four fins which collapse upon insertion into the circuit board hole. Although the four fins tend to collapse uniformly and accurately locate the contact within the circuit board hole, they do not have sufficient resiliency to maintain a relatively high retention force between the mounting portion and the circuit board hold.
Another type of contact includes a mounting portion which is flattened and split to form two branches separated like the eye of a needle that provide a resilient interference fit between the contact and the hole as described in U.S. Pat. No. 3,917,375. Although this contact advantageously requires a low insertion force and produces a relatively high retention force due to the spring action of the branches, the area of the contact engaging the hole is not sufficient to insure accurate location of the contact and does not provide for efficient heat transfer or secure electrical engagement.
U.S. Pat. No. 4,066,326 provides three resilient branches by twice splitting the mounting portion of the contact and separating the central branch in a direction opposite to that of the two outer branches. The three branches triangularly contact the circuit board hole and more positively locate the contact with respect to the circuit board than does the previous branched contact. However, the engagement area between the contact and the hole is still relatively small and does not provide efficient electrical engagement or heat transfer between the contact and the plated circuit board hole.
Another type of branched contact is described in U.S. Pat. No. 4,186,982 in which the mounting portion of the contact is sheared but the two branches thus formed are offset parallel to the shear plane rather than perpendicularly as in U.S. Pat. No. 3,917,375. This configuration is designed to create a high retention force, but does so at the expense of an undesirably high insertion force. In addition, the area of contact between the mounting portion and the hole is again relatively small.
In addition to the specific disadvantages associated with the various types of contacts and noted above, all of the contacts described thus far have a common disadvantage in that a relatively large mass of material must be availble at the mounting portions of the contacts in order to form the configurations which grip the circuit board hole. If the portion of the contact which extends above the circuit board for connection to an electrical device is to be thin and narrow, as is typically the case, material must be removed and discarded which causes machining expense and waste.
U.S. Pat. No. 4,155,321 discloses a contact which eliminates this waste by starting with a thin sheet and rolling the mounting portion into a resilient cylinder which is inserted into the circuit board hole. While this contact provides a low insertion force, a relatively high retention force, and a large engagement area between the contact and the circuit board, it is relatively expensive to manufacture because the rolling operation is difficult to perform and a large amount of material is necessary to form the cylinder.